Fan



W. T. DEAN Jan. 28, 1941.

FAN

Filed July 22, 1938 FIG. 1.

F IE. 2.

Patented Jan. 28, 1941 UNl TED STATES PATENT "OFFICE 5 Ametzl ffifixz gi l gt 220,812

3 Claims. (01. 230-209) This invention relates to improvements in fan, and more particularly to those which are adapted for operation when exposed to temperatures such as arev encountered in heating furnaces, although not limited thereto. 3

An object of this, invention is to provide a fan adapted to operate .in a furnace capable of maintaining temperatures in excessof 1400 degrees Fahrenheit for convection heating and-controlling the distribution of the gases throughout the furnace.

Another object is to "provide a fan or blower of heat resisting alloys so arranged as -to make all parts, subjected to heat, self-cooling to a point well withi n the safe limits of the alloys used.

Other {objects and advantages will become apparent-as the descriptionv proceeds, in which:

Figured is a transverse section of a convection heating furnace of the present invention; Figure 2 is a section on line 11-11 of Figure 1; 4 Figure 3 is a section on line III--III of Figure I .L ,-"Ffgure 4 is a section on line IV-IV of Figure 3; sea,

Figure 5 is a section on line V-V- of Figure 8. m the drawing, the numerals 2 and 3 represent the walls of a furnace which are constructed 'of' refractory insulating brick for heat conservation and quick heating. The furnace bottom 4 may be of any desired construction, such as car bottom, solid bottom or conveyer bottom type. In any case, metallic material to be heat treated is supported above the bottom 4 by suit-.

able alloy or refractory supports 5 of any desired construction, so as to permit the circulation of heated gases down through the material,

being treated and beneath the same in a horizontal direction, as indicated by the arrows in Figure 1, to the fan intake. The surplus gases are bled off at ttis oint through the dampered flues 6 into a main flue I to a stack connection (not shown) in the furnace wall.

The recirculated gases are exhausted from the furnace through the duct 8 into the fan rotor, to be more fully hereinafter described, and discharged therefrom at a high velocity into the short flue 9, discharging horizontally into the top (3f the furnace through the venturi shaped openng l0.

Gas or oil is fed through the pipe l2and mixes with air supplied through the pipe 14 to be combusted and mixed with the recirculated gases for discharge into the furnace through the Venturishaped openin "I. The opening I!) at the top of the furnace, being Venturi-shaped, supplements the velocity of the gases induced by the action of the fan rotor, so that upon entry into the upper portion of the furnace the gases have a high velocity. Combustion of the gases is completed in the-upper portion of the furnace which is separated from the heating chamber l5 by an arch shaped refractory partition memberlB. This partition member. I6 is provided with a plurality of perforations ll extending therethrough; sized and arranged within said member "5 so as toproyide for theuniform distribution of the products of; ,combust ion ata high 'velocity 7 into the heating chamber i5 and uniformly over the entire surface of thernetal being-heat treated.

The means forwithdrawing the gases from the 15 heating chamber and recirculating the same comprises a fan: constructed as shown in Figures- 3 through 5. Suitably mounted in the wall of said furnace, in any conventionaltype of bearing support I8, is a hollow ,;steel shaft l9 over which is closely fitted anouter tube 20 of asuitable heat resisting alloy. Tubular driving-arms, o't heat resisting alloy are welded at spaced intervals around the periphery of said tube 20. Impellers" 22, formed from fiat sheets of heat resisting alv are bent into U-shaped cross-section, as.

with the free ends thereof-1' loys, shown in Figure 4, forming a restricted duct or passageway 23 The u-shaped end portion of each impeller is provided with openings 24 in communication with the ducts or passageways 25 formed between the outside diameter of said tubular driving-arms 2| and the disks 26 and 21 which close the ends of said U-shaped impellers 22 by being welded thereto, as illustrated at 28. Suitable openings 29 and 30 in thehollow shaftl9 and outer tube 20, respectively, coincide with the ducts or passageways 25 to permit circulation of cool air which has been drawn in from the outside through the hollow steel shaft [9 so that the cool air will 40.

pass into the restricted duct or passageway 23 for discharge at the tip of said fan. Referring particularly to Figure 1 of the drawing, it will be perceived that the hot gases moving through the duct 8 will flow in the direction of the arrows upwardly between the outer surface of the disk As the hot gases move upwardly across "the-outer 2! and the adjacent inner surface of the furnace' wall, which is slightly spaced therefromk H surface of the disk 21 which, as {shown moi-e159 clearly in Figure'3, is of solid construction, they,

are drawn upwardlyinto' the-short flue 9 bythe air being discharged at the tip of the fan.

This-design withproximity-tothe desired point of dischargefor the hot gases permits-theme of relatively large diameters for the fan with low shaft speed, yet giving high velocity to the air and hot gases to be moved. I'he operation of the fan, which may be in any conventional manner to set up the required iiow of hot gases also sets up a flow of external cold air through the hollow shaft. This air is discharged at the fan tips, mixing with the hot gases, and, by the amount of air so passed, reduces the combustion air required without affecting the reducing atmosphere within the heating chamber. In a typical case it was found that with l per cent. of the required combustion air passed through the impellers as a cooling medium, the temperature of the impellers was limited to less than 1200 degrees Fahrenheit when handling gases at 1650 degrees Fahrenheit.

Since the fan of the invention is necessarily of the overhung type, the large diameter hollow shaft operating at low shaft speed is ideally suited to the required service as it eliminates bearings in the bath of hot gases. Preferred bearings are of the synthetic-resin-cotton water-lubricated type, further tending to limit maximum temperatures to which the shaft may be subjected.

Combustion air for furnaces of the type hereindescribed must be supplied under slight pressure to assist in the recirculation action and'to provide for complete combustion control. 1

In a furnace of the' type described, the overall thermal efficiency may be extremely high-due to rapid even heating of the" charge coupled with excellent insulation and good recuperation, while surface scaling and alteration in grain size may be strictly limited: the first by entire absence of free oxygen, the latter by limited maximum temperatures and short treating time.

While I have shown and described specific embodiments of the invention, it will become apparent that I do not wishto be limited exactly thereto, since various modifications may be made without departing from the: scope of the invention, as defined by the appended claims.

member and a U-shaped outer tip member, said innermost member forming with the spaced plates passageways in alignment with the said spaced openings in said hollow shaft, whereby cool air, is directed only to the tip of each of said impeller blades.

2. A fan comprising a hollow shaft having circumferentially and axially spaced openings, spaced parallel plates secured to said hollow shaft, and heat-resistant impeller blades positioned between said spaced plates and arranged radially about said hollow shaft, said impeller blades including closed tubular members'secured to said shaft between said axially spaced openings to form with said spaced-plates passageways in alignment with the spaced openings in said hollow shaft, and U-shaped tip members secured to said closed tubular members and said spaced plates and provided with openings in communication with said passageways so as to direct cool air to the tip of each impeller blade.

3. A fan comprising a hollow shaft, a plurality of impeller blades secured between parallel spaced plates and-radially disposed about said hollow shaft; each of said impeller blades having a closed chamber terminating inwardly of its outer end, and means disposed exteriorly of said chambers but between said parallel spaced plates for permitting the passage of air to the outer ends of said impeller blades, said hollow shaft having apertures communicating with said means.

WILLIAM T. DEAN. 

